Inactivated Polio Virus vaccine (IPV) is approved by FDA and is becoming more popular as a childhood vaccine, in addition to Oral Polio Vaccine (OPV). CBER of FDA has the responsibility of testing the potency of different lots of IPV produced by various manufacturers to strictly regulate the lot-to-lot variability of different IPV vaccines to make a safe and effective dose of the vaccine available to genneral public. The potency of IPV is the amount of D-antigen present in a given vaccine preparation and is determined by either a monkey serological test or an ELISA assay using type-specific monoclonal or polyclonal antisera. Previous studies with monoclonal antibodies in ELISA tests warranted improvement of the reagents or standardization of alternative ELISA protocols. In this project, research is being pursued in order to develop an improved potency assay for IPV using polyclonal antisera. Three type-specific antisera are being developed in rabbits to be used as the capture antibodies and three type-specific antisera are being developed in sheep to be useful as detection antibodies in the ELISA procedure. The immunogens for these sera are wild-type, live, infectious Polio Virus Types I,II and III and are purified by CsCl2 gradients and will be enriched for the protective D-antigens. Appropriate methods and protocols are developed to first optimize and then to standardize the ELISA protocol to be useful as a validated, routine lot release potency determination method available at CBER.